Process for polymerizing vinyl chloride



Patented June 17, 1952 PROCESS FOR POLYMERIZING VINYL CHLORIDE Marcel L.Sans, Venissieux, France, assignor to Societe Anonyme des Manufacturesdes Glaces et Produits Chimiques de Saint-Gobain,

Chauny & Cirey, Paris, France No Drawing. Application July 2, 1947,Serial No. 758,666

3 Claims. 1

This invention relates to vinyl polymers and particularly to vinylpolymers composed wholly or partly of polyvinyl chloride. This inventionis a continuation in part of my prior applications Ser. Nos., 602,679,filed June 30, 1945 now U. 8. Patent 2,508,801, and 723,304, filedJanuary 21, 1947, now abandoned.

I have invented certain polymers of vinyl chloride and certaincopolymers of vinyl chloride that are possessed of superior qualities.These polymers are characterized by a high degree of polymerization, byhigh purity, by excellent dielectric properties, and by extraordinaryheat stability. These new compounds are made by a new process whichmakes possible bulk polymerization of vinyl chloride, the production ofa homogeneous powder without the crushing and grinding that hasheretofore been considered necessary, and the production of this powderin selected particle size without crushing or grinding even when acopolymer is made.

It is a major object of this application to describe these new vinylpolymers and copolymers and to set forth a method by which they may besuccessfully prepared. In considering the invention it should be kept inmind that the results obtained are secured by a process that is acombination of steps, several of which are individually new and capableof; contributing increments of improvement to other processes andtherefore having inventive novelty in themselves.

The primary rawv material involved in the invention is vinyl chloride,but the invention also extends to the polymerization of mixtures ofvinyl chloride with other polymerizable materials such as vinyl acetate,acrylic esters, and fatty acids and their salts, particularly theunsaturated fatty acids.

A characteristic of the new invention is the employment of a catalyst ofthe peroxide-persalt class, called peroxides herein the outstandingexamples of which are the organic peroxides, the persulfates, and theperborates. The amount of catalyst is such that the free oxygen does notexceed .015% of the weight of the monomer. Such an amount produces anunsatisfactory commercial yield except for the step of the process whichincludes in the reaction mass a salt of ,a strong base and a weak acid,in a small amount, examples of which are the alkali salts of weak acidsand the salts of carboxylic acids such as the cadmium, zinc and leadsalts thereof. It is preferable to carry out the polymerization in mostinstances in the presence of a small quantity of a.

weak acid or an anhydrid thereof. The reaction 5 is preferably carriedout in the absence of solvents or diluents.

A phase of the invention particularly valuable in the making ofcopolymers includes the regulation of the period of polymerization.

In order to demonstrate various phases of the invention a number ofexamples are given hereinafter which have been selected because theydemonstrate in a clear and comprehensible manner the nature of theinvention, the eificacy of a particular step, or the beneficial resultsas embodied in new and superior products. It must be remembered,however, that these examples are for illustrative purposes, are notlimitations, and that while they furnish evidence to support the generaldescription, they are not the only evidence that is available, or whichcan be turnished to support the application. It is not the function ofthe examples to duplicate statements found in the more general portionof the specification, nor is it the function of the general portion ofthe specification to duplicate material sufficiently set forth in theexamples. In carrying out the polymerization, excellent results wereobtained by a special autoclave having rotary stirrers of which an innerblade moves the polymerization mass out toward the wall of the autoclaveand a following, outer blade moves the part of the polymerization massthat is against the wall inward away from it, thus mixing and movingpart of the mass to a place of lower temperature and immediatelythereafter moving it away therefrom.

The catalysts used are from the peroxide-persalt class notable amongwhich are the organic peroxides and the salts such as persulfates andperborates. A standard catalyst of this class is benzoyl peroxide whichis available on the market at reasonable cost, is of excellent efficacy,and is usually employed. It will be referred to in the followingexamples, but'it is to be understood that this particular reference isnot a limitation but is adopted in order to keep the conditions andreagents as uniform as possible throughout the examples in order todemonstrate the effect produced by certain variations in process.Heretofore in order to obtain good results from polymerization, it wasnecessary to employ comparatively large amounts of catalyst. Forexample, when polymerizing vinyl chloride itwas necessary to employ acatalyst of the peroxide-persalt class having an active oxygen contenton the order of .04% of the weight of the monomer and frequently evenmore. That process had adequate difiiculty when ordinary processes ofpolymerizalevel throughout the operation.

tion were employed, but when it was attempted to undertake bulkpolymerization it was found that the reaction was accompanied by localoverheating, by extreme violence in the reaction, or on the contrary itsactual arrest, and that under some conditions a solidification of thereaction mass occurred. In order to overcome those inconveniences it wasproposed to carry out the reaction by heating at slowly increasingtemperatures, or to arrest the reaction when there still remained aconsiderable fraction of the monomer to be polymerized, or stillfurther, to operate in the presence of important quantities of solventsor diluents. Such methods did not produce wholly satisfactory resultsand the best products that could thus be produced could not be heated toa temperature of 190 to 200 degrees C. without disintegrating.Furthermore, they were generally of comparatively low degrees ofpolymerization, and when made, were not made in bulk.

According to this invention, I employ an amount of peroxide-persaltcatalyst containing less than .015% free oxygen based on the weight ofthe monomer, an amount which is insufilcient to give an acceptablecommercial yield by the process of the prior art. With this amount ofcatalyst I employ a substance capable of fixing any acid released duringpolymerization or aging or decomposition by precipitation, byneutralization, or by neutralization and precipitation. The amount ofcatalyst preferably employed contains about .005% of the weight of themonomer in free oxygen and a small amount of acid fixing substance. Theacid fixers or stabilizers are preferably the salts of strong bases andweak acids, such as the alkali salts of weak acids, particularly, whenorganic salts are employed the salts of unsaturated organic acids, ofwhich trisodium phosphate is an excellent example, and the salts ofcarboxylic acids, such as oleic, acrylic, linoleic, particularly theheavy metal salts thereof such as cadmium, zinc, and lead. The acetatesof such salts are particularly convenient. When benzoyl peroxide isemployed a quantity equal to .08% of the monomer produces a satisfactoryquantity of free oxygen. In addition to the acetates, the oxalates andformates are also useful and are readily available.

In carrying out the reactions with the small quantity of catalyst plusthe stabilizer, it is now possible, even when operating in bulk, tocarry the temperature of the reaction to a relatively high levelimmediately and to maintain it at that For example, temperatures on theorder of 30 to '70 degrees C. have been successfully used under variousconditions. Thus operating, polymerizations from 85% complete to whollycomplete have been carried out in periods of time from 13 to 48 hours,which shows a reduction in time of treatment for given cases of 50% ormore.

In order to further facilitate the process, it is advisable to add tothe reaction an activator from the class of weak acids and theiranhydrids. It has hereinabove been pointed out that the acid released bydecomposition of the monomer or polymer is harmful. It is thereforeastonishing that the presence of an additional quantity of acid shouldnot be harmful. Nevertheless. this is the fact and it is part of myinvention to add a small quantity of such an activator to the reaction.Their presence reduces the time of polymerization when the amount ofcatalyst set forth hereinabove is employed or it permits one, by usingthe same periods of time. to further reduce the amount of catalyst. Itis advisable to incorporate the monomer, the catalyst, and thestabilizer thoroughly and to heat them until they are under pressurebefore adding the activator.

The polymerization of vinyl chloride and its copolymers begins not withan immediate setting but with a period of induction in which noobservable change takes place in the monomer and which is followed by aperiod of active transformation to the polymeric state. The period ofinduction is short or long, depending upon the nature of the monomer andthe conditions under which it is polymerized, but in each instance thereis a natural duration of the period of induction and of the period ofactive polymerization which is, in the case of vinyl chlorideparticularly, quite extensive. The difference between the rate ofpolymerization of vinyl chloride and, for instance, vinyl acetate isvery great so that when they are polymerized together polymerizationdoes not proceed evenly to a common end point, but at different rates todifferent end points which may be many hours apart. This complicates theprocess of making copolymers, and the products produced are of a grademuch inferior to those that are produced by this invention. For thesereasons and others, it is desirable to regulate the duration of theperiod of induction and to regulate the duration of the period ofpolymerization of compounds that are to be copolymerized so that theymay be brought to approximately a single end point and thus made tocontribute valuable qualities to a superior product. Thus, taking anytwo vinyl compounds that are to be copolymerized and which polymerize atdifferent rates, it is desirable to selectively slow down the rate ofpolymerization of the one which polymerizes fast and to hasten thepolymerization which proceeds more slowly. This action should beselective, either one or the other being applicable, or bothacceleration and slowing may take place together.

The quantity of catalyst present in this invention is so small that anymaterial added for the purpose of accelerating or slowing the period ofinduction, the period of active polymerization, or both, must be inertto the catalyst and must not interfere with the operation of thestabilizer. I-Ieretofore, attempts have been made to reduce the periodof induction and the total period of polymerization, or to extend it,but so far as known, every additive of this type has had an undesirableeffect upon the catalyst.

Not only is it desirable to accomplish speed control of thepolymerization of mixed monomers, but it is desirable to be able to havecontrol of the period of induction, the period of active polymerization,and the total period of polymerization where single monomers are inprocess.

In order to reduce the total duration of an operation or to furtherreduce the quantity of catalyst while employing the same duration, thevinyl compounds are'passed in monomeric form and in gas phase overactive carbon heated to temperatures between 30 and degrees C. prior topolymerization. The following examples illustrate this phase of theinvention.

Example 1 250 kg. of vinyl chloride monomer were treated with 20 kg. ofactive carbon at 45 degrees C. and then mixed with 1 kg. of acetic acid,2 kg. of lead acetate, and grams of benzoyl peroxide and heated to 55degrees C. in the special autoclave. After 13% hours the rate ofpolymerization was 50%, giving an hourly rate of 4.35%. The product hada specific viscosity of 1.90. The product was an excellent fine powder.

Example 2 250 kg. of vinyl chloride were treated with the same activecarbon as in the preceding example at a temperature of 40 degrees C. andmixed with 2 kg. of acetic acid, 2 kg. of lead acetate, and 150 grams ofbenzoyl peroxide and heated at 55 degrees C. for 19 hours, minutes,after which the polymerization was 85.8% complete, representing anhourly rate of 4.9%. The product had a specific viscosity of 1.85 andwas in the form of a good powder.

Example 3 250 kg. of vinyl chloride were treated as in the two precedingexamples at a temperature of 45 degrees C. It was then mixed with 1 kg.acetic acid, 2 kg. lead acetate, and only 100 grams of benzoyl peroxide,which is only 04% of the monomer. The mass was heated at 55 degrees C.for 18 hours after which the extent of polymerization was 72%,representing an hourly rate of 4%. The powder obtained was fine andwithout lumps.

Example 4 250 kg. vinyl chloride were passed over active carbon underthe conditions provided and were polymerized with the assistance of 100grams (04%) of benzoyl peroxide. A fine powder was obtained which, afterworking in a roll mill, remained 8 minutes at 190 degrees C. under 250kg. of pressure without decomposition, whereas .08% of benzoyl peroxidewas required to produce the same yield in the same time according to themethods of the prior art, and the product thus produced by the prior artmethods was worked up in the roll mill, but was stable for only twominutes under the said conditions.

It is apparent from the foregoing examples that in spite of the smallquantity of catalyst a high hourly yield is obtained of a fine powderousproduct. It is also apparent that the duration of heating is reduced. Onthe other hand, the process permits a material reduction in the quantityof catalyst.

The new products that are produced by this invention are superior inmany ways, but possibly their most outstanding quality is their heatstability. Similar products made by the process of the prior art are notstable under identical circumstances for more than 1 or 2 minutes at amaximum. The process itself has the advantage that the heating can bevigorously commenced at the most favorable temperature from thebeginning of the reaction without danger of the reaction proceeding tooviolently and producing degraded products.

Another advantage is that there is directly obtained a polymerizedproduct that is substantially free of residual catalyst and isconsequently purer and better. Only small quantities of additionalsubstances are employed to fix the acid disengaged during the reactionand some of these remain in the reaction mass and are capable of fixingany products of decomposition that may be formed during use. Thereaction is calmer than those which have been previously known and isunder better control than has ever been possible heretofore. Thefinished products are purer and are more resistant to chemical agents 6than the prior art products. They have excellent dielectric qualities.

The polymers of the invention have a molecular weight between 50,000 and90,000 by the viscosimetric method.

The process is particularly advantageous in that the necessity ofgrinding a solid or lumpy product to produce a powder is totallyeliminated and a powder or a product of given particle size can beproduced at will in a special autoclave. This advantage is particularlynoted in the case of copolymers which have heretofore had a pronouncedtendency to form into aggregates in the reaction vessel. Anotherparticular advantage is that the bulk polymerization of vinyl chlorideand its copolymers can be carried out, which was heretofore believed tobe impractical.

As many widely different embodiments of the present invention may bemade without departing from the spirit and scope thereof, it is to beexpressly understood that the same is not limited to the specificembodiments, except as defined in the appended claims.

What is claimed is:

1. The method of making vinyl polymers that includes the steps ofpassing vinyl chloride in gas phase over active carbon, heating thevinyl chloride in confinement in the absence of solvents and diluents toa mean temperature in the range 30-70" C., for not materially more than48 hours while mixing it and moving portions of it to a place of lowertemperature and immediately away from said place into the mass again inthe presence of a peroxide catalyst containing not over 015% of theweight of the monomer of free oxygen, and of a stabilizing amount of asalt of an acid capable of reacting with HCl.

MARCEL L. SANS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,920,403 Klatte et al. Aug. 1,1933 1,997,145 Herbert Apr. 9, 1935 2,122,805 Wulif et al. July 5, 19382,157,997 Brous May 9, 1939 2,218,645 Japs Oct. 22, 1940 2,365,400Fikentscher Dec. 19, 1944 2,365,506 Alexander Dec. 19, 1944 2,387,571Fikentscher Oct. 23, 1945 2,406,403 Rogers Aug. 27, 1946 2,412,504Goldfinger Dec. 10, 1946 2,423,388 Jordan July 1, 1947 2,508,801 SansMay 23, 1950 FOREIGN PATENTS Number Country Date 2,627 Australia of 1926OTHER REFERENCES Brajnikofl: Plastics (London), March 1942, pp. 72-78.

Houwink: Chemie Und Technologie Der Kunstuif, vol. II, page (EdwardsBros., 1942).

1. THE METHOD OF MAKING VINYL POLYMERS THAT INCLUDES THE STEPS OFPASSING VINYL CHLORIDE IN GAS PHASE OVER ACTIVE CARBON, HEATING THEVINYL CHLORIDE IN CONFINEMENT IN THE ABSENCE OF SOLVENTS AND DILUENTS TOA MEAN TEMPERATURE RANGE 30-70* C., FOR NOT MATERIALLY MORE THAN 48HOURS WHILE MIXING IT AND MOVING PORTIONS OF IT TO A PLACE OF LOWERTEMPEATURE AND IMMEDIATELY AWAY FROM SAID PLACE INTO THE MASS AGAIN INTHE PRESENCE OF A PREOXIDE CATALYST CONTAINING NOT OVER .015% OF THEWEIGHT OF THE MONOMER OF FREE OXYGEN, AND OF A STABILIZING AMOUNT OF ASALT OF AN ACID CAPABLE OF REACTING WITH HCL.